Sound-reproducing system



Jan. 29, 1929.

J. L. REYNOLDS SOUND REPRODUCING SYSTEM 2 Sheets-Sheet 1 Filed May 24, 1927 A/Iomz/e Raf/'0 of m 20 ww/ Jo /7d 2000 Freyuency J. LaQ gwcvNoLbs INVENTOR ATTORNEY Jan. 29,- 1929.

1,700,450 J. L. REYNOLDS scum) REPRODUCING SYSTEM Filed May 24; 1927 2 Sheets-Sheet 2 J. Lou s fiavuogps INVENTOR fill/011i ATTORNEY Patented Jan. 29, 1929.

TES.

J. LOUIS REYNOLDS, OF LONG ISLAND CITY,

1,700,450 PATENT OFFICE.

NEW YORK, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO ELECTRICAL RESEARCH PRODUCTS, INC., A CORPORATION OF DEL- AWARE.

Application filed May 24,

This invention relates to electrical controlling systems and apparatus, and 1n particular to methods and means for controlling artificial "sound reproduction.

In sound recording and reproducing systems employing mechanical media sound records such, for example, as the well-known wax disc type, because of the mechanical characteristics of the disc material itself and partly because of the methods of engraving a record inthe disc, there are introduced extraneous characteristics which are detrimental to proper reproduction. These undesirablemechanical imperfections in the disc" material give rise in the reproducing process to what may be generally described as surface noise. Itis well known in artificial reproducing systems employing this type of record that the deleterious effects of surface noise are not constant throughout the frequency range of the sounds reproduced. It has been found that the surface noises themselves have --a frequency range which is most, predominant and objectionable above 2000 cycles per second. It is alsoknown that a certain amount of surface noise may be present in a reproduced program without materially affecting the pleasing quality of the reproduction. In other words, while the proportion of undesirable characteristics in the wax record to the sound record characteristics is a fixed quantity so far as'eachindividual record is concerned, in the reproducing process the relative proportions so far as their effect on the reproduced program is concerned, varies with the volume of reproduction required. That is to say, we may characterize the inherent surface characteristic of the record materialitself as manufacturedsurface noise which, during the reproducing process, gives rise to reproduced surface noise. ratio of the reproduced surface noise to the actual program to be reproduced must never exceed a predetermined value if the pleasing quality of the program is not to be marred.

It has been ound that this so-called allowable ratio of surface noise toprogram varies with the general level of volume at which the reproducing system is operated. Heretofore means have been proposed for reducing the effects of surface noise on the reproduction by employing fixed electrical net- Works or equalizers, by means of which the As hereinabove mentioned, the- SOUND-BEPRODUCING SYSTEM.

1927. Serial No. 193,862.

proportionate effects of surface to actual program are constant, and the maximum allowable ratio is reached at a certain volume level. Above that level the ratio of surface noise to sound program must be reduced if a pleasing reproduction is to be maintained, that is, the sound currents must be subjected to greater equalization. Equalization of this character results in the sacrifice of certain frequency components in the reproduction sounds. For very low volume reproduction actual ratios of surface noise to sound program may be much higher than for loud volume reproduction, that is to say, for low volume reproduction, the necessary equalization is less than for loud volume reproduction. Consequently, fg r low volume reproduction using a,,fixed equalizer for surface noise, the over-all frequency distortion for a given record is a minimum. As the volume of reproduction is increased this distortion of reproduction. Hence, to maintain the most desirable quality of reproduction at any if desired volume, means must be provided for accordingly varying the degree of equalization.

It is therefore one of the principal objects of the present invention to provide an electrical sound reproducing system wherein the allowable ratio of surface noise to desired sound is varied in accordance with the volume of reproduction.

A feature of the invention relates to the means for varying the characteristics of an equalizer in accordance wtih the desired volume of reproduction.

A still further feature of the invention pertains to means for simultaneously vary ing the gain of a sound reproducing amplifier and for adjusting the characteristics of a surface noise equalizer.

A further feature of the invention relates to an artificial sound reproducing system using mechanical media sound records and adjustable electrical networks which may be varied .by a single manipulation to maintain in a sound reproducer the faithfulness of reproduction independent. of volume.

Other features and advantages not specifiin which the allowable ratio of surface noise todesired sound varies with the volume of sound produced by an electro-mechanical sound reproducer.

Fig. 2 shows a series of curves illustrating the gain-frequency characteristics of a reproducing system at various volume levels.

--Fig. 3 shows the invention as applied to a reproducing system employing disc type records.

Figs. 4 and 5 are modifications of the system disclosed in Fig. 3.

In artificial sound reproducing systems employing mechanical media sound records, it 1s desirable that the sound cutting in the record blank material vary solely in accordance with the characteristics of the sounds to be reproduced. Two methods for recording sounds in this type of record blank are known respectively, as the lateral cut method and the 11111 and dale method. Whichever type of record is desired it is the usual practice to form the 'groove by means of a cutting tool which is actuated by a sound responsive device. At times, due to-imperfections in the master record surface; for example, that due to varying degrees of hardness at different points on the surface as well as that due to the uneven surface structure of the material itself, it is not always possible to produce a cutting which has char acteristics faithfully corres onding to the sounds recorded. It will e appreciated, therefore, that in the recording process alone, the master record will show variations in sound cutting which bear no relation to the soundbeing recorded. In the intermediate process between the actual cutting and the ormation of the final wax record, other causes are eflective to produce additional undesired surface characteristics so that in the actual record blank as used for reproduction, the surface of the sound cutting may under microscopic examination, show pear to predominate.

This variation is shown by curve .100 in Fig. 1 of the drawin wherein it is seen that the allowable ratio 0 surface noise to useful sound, so far as an auditor is concerned, must be least when the total volume of sound; is a maximum, and conversely, the allowable ratio may be comparatively larger when the volume approaches zero.

The actual ratioof surface imperfections.

to sound cutting is, for a given record, fixed, but as pointed out hereinabove, the efiects so far as reproduction is concerned, are a function of the volume of sound required,

and the allowable ratio during reproduction varies. The manner in which this allowable ratio varies is illustrated in the curve of Fig. 1 wherein the ordinates represent volume of reproduced sound expressed 111 terms of amplifier gain, and the abscissae represent the V allowable ratio of surface noise to useful sound. From an inspection of Fig.1 it will be seen that at high volume reproduction, I

sets of curves representative of the manner in which the transmission amplifyin system must be varied atdiiferent volume evels.

The ordinates of the curves of Fig. 2 represent de rees of reproduction volume in terms of amp ifier gain, while the abscissae represent frequencies of the component amplified currents. Were the record surfaces free from imperfections, the corresponding characteristics of the transmission system for faithful reproduction would obviously be straight, as represented by curves A, B and C of Flg. 2. As pointed out hereinabo've, however, the mechanical imperfections or surface noise in the record, while substantially negligible in the lower end of the frequency s ectrum, begins to assume prominence as the frequenc rises above 2000 cycles per second. Accor ingly, the transmission characteristics of the amplifying system must drop off as the higher frequencies are passed. For example, for low volume reproduction, it will be necessary to adjust the constants of the amplifier network to give a transmission characteristic represented by curve A. Similarly, for medium volume reproduction, the network would have to producethe characteristic represented by curve B, and simi larly for largevolumes. An well-known type of attenuating network or producin t e characteristics desired may be employe typical networks for producing these characteristics being illustrated in Figs. 3, 4 and 5 .of the drawing. Heretofore, equalizing networks of this character have been used, but these networks have generally been designed to effect equalization at only a particular volume of reproduction. By the present invention this equalization is made variable so that, as the volume is increased, the amount of equalization is correspondingly increased to take care of the increasing effects of surface noise.

Referring to Fig. 3, the invention is shown applied to a sound reproducing system of the general character disclosed in my co ending application Serial No. 180,323, filed pril 1, 1927. The numeral 1 represents a phonograph turntable upon which is mounted for rotation therewith the wax disc 2 having a continuous cutting thereon corresponding to the sound to be reproduced, saidcuttlng be-- ing preferably of the lateral type. An electromechanical translating device 3 is adapted to be actuated by the associated stylus 4 and generates voltages corresponding to the varying degrees of cutting in the record blank surface. These currents are then impressed upon the terminals of the artificial line AL which may be of the character disclosed in my application Serial No. 180,323 hereinabove referred to. The currents passing through the artificial line are more or less attenuated according to the length of line included in circuit with the device 3 and the input circuit of the electron discharge amplifier. This input circuit is associated with the line AL by means of the brushes 5 and 6 which may be moved to vary the attenuation. For a description of the manner in which an artificial line of the character shown may be utilized to control the energy level of the sound-modulated currents reaching the amplifier 7, reference may be had to my copending application Serial No. 180.323. For the present descriptionit will suflice to say that the amplitude of the currents reaching the input circuit of the amplifier 7 decreases as the brushes 5 and 6 are moved towards the right, away from the terminals 8, 9.

For the present it will be assumed that the brushes 5 and 6 have been adjusted to the extreme left-hand position so that the currents in the output circuit of amplifier 7 have their maximum value for the purpose of operating the reproducer 10 at the loudest degree of volume. Accordingly, the allowable ratio of surface noise to useful sound is small and the difierent frequency components must be transmitted to reproducer 10 according to curve C of Fig. 2. For the purpose of thus attenuating the higher frequency components, a combination of electrical elements such as disclosed in United States patent to G. A. Campbell, No. 1,227,113, of May 22, 1917, may

be employed. One form of network for this.

purpose is disclosed in Fig. 3 and comprises the variable inductance 11 and the variable capacitance 12. While in the drawing separate adjustments are indicated for varying the capacity and inductance, it will be understood that the values of these elements may be so chosen that the currents from the amplifier 7 may be attenuated in accordance with curve C by a single adjustment.

- Should it be desired to operate the reproducing system at a lowervolume level, brushes 5 and 6 are moved toward the right to correspondingly reduce the energy level of the currents reaching amplifier 7. As mentioned I above, at low volume reproduction less surface noise equalizatlon is required, so that inductance 11 and 12 may be varied to give.

anov'er-all transmission characteristic represented by curve A. Brushes 5, 6 andthe in-" ductance 11 and capacity 12 are preferably provided with suitably calibrated scales so that an attendant may adjust the brushes 5, 6 to give the desired volume of reproduction and at the same time adjust the inductance and capacity to corresponding values.

Fig. 4 of the drawing shows a' network and amplifier for producing variable equalized volume-transmission characteristics similar to those obtained with the apparatus of Fig.

adjustment of this shaft the volume of repro duction and the equalization for volume-frequency distortion may be controlled.

Fig. 5 shows an arrangement similarto that of Fig. 4 except that the electrical elements of the amplifier-network are connected in shunt with the current source. In this figure also it is preferable to have all the electrical elements arranged for simultaneous adustment by a single manipulation.

While in the foregoing description and in the drawings the invention is disclosed in connection with a reproducing system employing one particular type of sound record, it is to b understood that the invention is equally applicable to systems using other types of records which, because of their mechanical or structural characteristics, tend to introduce undesirable noises into the reproduction. For example, in systems using photographic film records and light responsive devices, due to the non-homogeneity of the crystalline structure of the photographic emulsion, varying thicknesses. of film and othersimilar causes, variationsareintroduced into the response of the light-sensitive device which have no relation to the actual sound recorded. These undesirable variations are of the same character and may be equalized in a similar manner to the variations in the ployed in its most generic sense. Furthermore, while there is shown a specific type of network for equalizing for volume-frequency distortion, it is understood that the disclosure is essentially schematic in this respect, as any form of equalizer may be employed without departingfrom the spirit and scope of the invention.

What I claim is:

1. In a sound recording and reproducing system, means for artificially generating sound modulated currents, an electron discharge device for amplifying said currents, means for varying the gain of said device, a Variable electrical net work for variably attenuating the frequency components of said currents, and means for adjusting the gain of said amplifier and for simultaneously adjusting said net work.

2. In an artificial sound reproducing system, an element having a surface cutting to correspond 'with sounds to be reproduced, means for translating said cutting into corre' sponding electric currents, said currents having undesirable characteristics corresponding to the surface characteristics of said element, means for amplifying said currents, a sound reproducer operated in accordance sounds to be reproduced, a device for translating said record into corresponding electric-currents, a sound reproducer controlled by said currents, an electron dischage amplitier, a network for selectively attenuating the compo nents. of said currents and means effective by a single adjustment to vary the gain of said amplifier and for simultaneously varying said network in accordance with the variation in gain to preserve the faithfulness of reproduction at any desired volume.

4. In a sound reproducing system, the combination of an element carrying a record of sounds to be reproduced, means for translating said record into corresponding electric currents, said currents having undesirable characteristics corresponding to physical characteristics of said element, means for amplifying said currents, a sound reproducer operated in accordance with said currents, and means for varying the attenuation of the frequency components of the amplified currents according to their degree of amplification.

In testimony Whereof,I have signed my name to this specification, this 20th day of May, 1927. p

J. LOUIS REYNOLDS. 

